This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Although few simian rotaviruses (RVs) have been isolated, such strains have been important for basic research and vaccine development. To explore the origins of simian RVs, the complete genome sequences of strains PTRV (G8P[1]), RRV (G3P[3]), and TUCH (G3P[24]) were determined. This data allowed the genotype constellations of each virus to be determined and the phylogenetic relationships of the simian strains with each other and with non-simian RVs to be elucidated. The results indicate that PTRV was likely transmitted from a bovine or other ruminant into its host of origin (pig-tailed macaques), as its genes have genotypes and encode outer-capsid proteins similar to those of bovine RVs. In contrast, most of the genes of rhesus-macaque strains, RRV and TUCH, have genotypes more typical of canine-feline RVs. However, the sequences of the canine/feline-like genes of RRV and TUCH are only distantly-related to those of modern canine/feline RVs, indicating that transmission of the progenitor virus from a canine/feline host to a simian host was not recent. The remaining genes of RRV and TUCH appear to have originated through reassortment with bovine, human, or other RV strains. Finally, comparison of PTRV, RRV, and TUCH genes with those of the vervet-monkey RV SA11-H96 (G3P[2]) indicates that SA11-H96 shares little genetic similarity to other simian strains and likely has evolved independently. Collectively, our data indicate that simian RVs are of diverse ancestry with genome constellations that originated largely by interspecies transmission and reassortment with non-human animal RVs.